The 645E is of relatively recent vintage, so it wouldn't be as bad as a 40+ year old camera that had sat unused for a long time.

Does it have the standard hand crank, or the thumb operated "rapid" winder, or both?

Check the camera and lens for signs of excessive dirt, visible migrating lubricant, excessive wear, mould or battery leakage/corrosion. If you don't see any of these problems, and the camera appears to function well with film in it, as long as you budget for a CLA, it should end up to be a good choice.

“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2